I tried with “then link” that takes away teh red error from the Request Builder but then same arror when debug in the Json Deseralize activity
surround the endpoint with "

check what it is returned in detail e.g. by using Response_Content within the immediate panel
maybe it is a JArray and starts with [ so we would use Deserialize JArray
feel free to share with us a screenshot from the immediate panel output
also check the returned status
otherwise, use JSONLint for JSON validation
UPD1 - edit after API check




